S.D. Codified Laws § 25-7A-21.1

In any order establishment case, the custodian is limited to a prior-period support obligation or arrearage not exceeding three years before either the date of application with any Title IV-D agency, the date of filing with a court of competent jurisdiction, or the date of a written demand served personally or by registered or certified mail, return receipt requested, upon the noncustodial parent at the noncustodial parent's last known address, whichever occurs earlier.